TYPES OF CHEMICAL REACTIONS

Why identify reaction types? It is important to be able to identify reaction types because it allows you to predict the products of a reaction. Most simple chemical reactions follow one of five patterns.

1. Synthesis reaction ONE PRODUCT is formed from two or more reactants. The reactants can be elements or compounds. General formula: A + X  AX Also called a combination reaction.

Examples of synthesis rxns. 2 H2 + O2  2 H2O 2 K + Cl2  2 KCl H2O + N2O5  2 HNO3

Na (s)

Cl2 (g)

2 Na (s) + Cl2 (g)  2 NaCl (s)

2. Decomposition Reaction ONE REACTANT breaks down to form two or more products. The products can be elements or compounds. General Formula: AX  A + X

Examples of decomposition rxns. 2 H2O2  2 H2O + O2 H2CO3  H2O + CO2 2 HgO  2 Hg + O2

Decomposition of nitrogen triiodide 2 NI3  N2 + 3 I2 Make sure volume is on. Click here.

3. Single Replacement Rxns An element reacts with a compound (usually ionic) and takes the place of the element it is most similar to. A metal will replace a metal. A nonmetal will replace a nonmetal. General formulas: A + BX  B + AX (A is a metal) Y + BX  X + BY (Y is a nonmetal)

Examples of single replacement rxns. Mg + 2 AgNO3  2 Ag + Mg(NO3)2 Cl2 + 2 KBr  Br2 + 2 KCl 2 Al (s) + Fe2O3 (s)  Al2O3 (s) + 2 Fe (l) The above equation represents the "Thermite Reaction"

4. Double Replacement Rxns Two compounds (usually ionic) react and exchange ions with each other. REMEMBER: Positive ions want to “hang out” with negative ions. Typical result is the formation of a precipitate, formation of a gas, or formation of water. General formula: AX + BY  BX + AY (A and B are metals)

Examples of double replacement rxns. CaCl2 + Na2CO3  2 NaCl + CaCO3 2 HCl + Na2S  2 NaCl + H2S NaOH + HNO3  H2O + NaNO3 Pb(NO3)2 + 2 KI  2 KNO3 + PbI2

Examples of double replacement rxns. Ex. Solutions of potassium sulfate and calcium bromide are mixed. Ex. Solutions of hydroiodic acid (HI) and calcium hydroxide are mixed. Ex. Solutions of magnesium nitrate and potassium phosphate are mixed Ex. Solutions of lithium carbonate and copper (II) acetate are mixed.

5. Combustion Rxns The fast reaction between a substance and oxygen gas; also called burning. If the substance is made of carbon and hydrogen (or carbon, hydrogen, and oxygen), the products of the reaction will be carbon dioxide and water. Some synthesis reactions are also combustion reactions.

Examples of combustion rxns. CH4 + 2 O2  CO2 + 2 H2O C4H9OH + 6 O2  4 CO2 + 5 H2O 2 Mg + O2  2 MgO

THE END

Single replacement with hydrogen When some metals react with water or acids, a single replacement reaction may occur. In both cases, the H (from the water or from the acid) acts similar to a metal; the metal will replace the hydrogen. For single replacement reactions with water, it is helpful to think of the water as HOH.

Single replacement with hydrogen Ex. Potassium metal is added to water. K + H2O  KOH + H2 2 K + 2 H2O  2 KOH + H2 Ex. Calcium is added to hydrochloric acid, HCl. Ca + HCl  CaCl2 + H2 Ca + 2 HCl  CaCl2 + H2